The present invention relates to an overcurrent protection arrangement, to a method for protecting an electric element from an overcurrent, and to a means of transportation.
One regulation regarding electronic aircraft components stipulates that the respective terminals be protected from short-circuits. These short-circuit currents can exceed several 100 Ampere and consequently destroy the electric devices in question because this causes said devices to be subjected to a multiple of their normal load. These high overcurrents can be created because the internal resistance of the electric components in aircraft needs to be maintained as low as possible so as to achieve the highest degree of efficiency possible.
Although the high short-circuit currents are shut down within a few milliseconds, each electronic device in the circuit needs to be checked as to its capability to withstand the applied short-circuit currents. A decisive factor in this case is the weakest internal electric component of the electric device. Since the load limit of this weakest component frequently does not suffice for withstanding the short-circuit current, it is possible that the entire device is damaged. Consequently, additional precautions need to be taken in order to lower the overcurrent below the load limit of the weakest component. The costs of these precautions drop as the load limit of the weakest device increases in case of a short-circuit. However, the utilization of more robust devices with a higher load limit is frequently limited by the technology to be used or design specifications, for example, volumetric or weight restrictions.
One known precaution for protecting an electric device is the utilization of a disposable fuse that interrupts the circuit in case of a short-circuit current without creating smoke or fire during a short-circuit. However, the utilization of these fuses should be avoided in aircraft applications because they are difficult to access for being repaired or replaced.
Another approach consists of reducing the overcurrent in the circuit. In a circuit that operates within alternating current, this is usually achieved with a coil. This coil increases the internal resistance of the electric device and thusly limits the intensity of the short-circuit current. However, since the normal load, for example, of heating devices in aircraft may exceed 1.5 kVA, the coil needs to be designed such that it is able to permanently withstand a current intensity of 12 Ampere. In order to also maintain the loss as low as possible, it is necessary to use large wire diameters that, however, result in a high weight, namely because the coils primarily consist of copper and may contain a core of a ferromagnetic metal.